Materials such as germanium (Ge), antimony (Sb), and tellurium (Te) are often deposited onto substrates as phase change memory materials for use in semiconductor wafers or other semiconductor device structures. The conformal deposition of such materials in the forms of GST films is desirable for use in semiconductor device structures having high aspect ratio topographical features such as vias. The deposition is often effected using CVD (chemical vapor deposition) or other processes.
The processing and handling of Ge, Sb, and Te materials for applying the GST films using CVD normally occurs at substrate temperatures above about 300 degrees C. The reason for this is that typical precursors for CVD processes generally utilize such high temperatures to promote molecular reactivity. However, amorphous or partially amorphous GST films are desired to attain the conformal deposition of the films and thus the substrate process temperature is preferred to be below the GST crystallization temperature, which is generally less than about 300 degrees C. This is specifically true for (1) GST in which the composition is stoichiometric (% Ge+% Sb*1.5=% Te); (2) GST with low levels of impurities; and (3) GST for use in devices having technologically desirable fast speed operations.
Processes of these types for GST deposition using CVD techniques at temperatures below 300 degrees C. in order to obtain amorphous GST or close to amorphous GST (partial crystalline) have heretofore been unknown, especially for achieving high Te content. This is due to the fact that Te precursors (when Te is incorporated in a CVD process) are difficult to activate and only have suitable reactivity at temperatures typically higher than 300 degrees C. Currently, it has heretofore not been possible using conventional CVD techniques to process amorphous or partial amorphous GST having compositions in which Ge:Sb:Te is about 4:1:5 or 2:2:5 in which the Te is as high as 50% or 56%, respectively. In addition, because conventional CVD techniques utilize precursors in the deposition of the GST at processing temperatures of 300 degrees C. and above, the deposition of the GST film generally results in the crystallization of the film and thus is typically not conformal, particularly when the Te is present in amounts above about 45%.